Shan Dou (from left), Jonathan Ajo-Franklin, and Nate Lindsey were both on a Berkeley Lab team that used fiber optic cables for detecting earthquakes and other subsurface activity.

Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have shown for the first time that dark fiber – the vast network of unused fiber-optic cables installed throughout the country and the world – can be used as sensors for detecting earthquakes, the presence of groundwater, changes in permafrost conditions, and a variety of other subsurface activity.

In a pair of recently published papers, a team led by Berkeley Lab researcher Jonathan Ajo-Franklin announced they had successfully combined a technology called “distributed acoustic sensing,” which measures seismic waves using fiber-optic cables, with novel processing techniques to allow reliable seismic monitoring, achieving results comparable to what conventional seismometers can measure.

“This has huge potential because you can just imagine long stretches of fibers being turned into a massive seismic network,” said Shan Dou, a Berkeley Lab postdoctoral fellow. “The idea is that by using fiber that can be buried underground for a long time, we can transform traffic noise or other ambient vibrations into usable seismic signals that can help us to monitor near-surface changes such as permafrost thaw and groundwater-level fluctuations.”

Dark fiber refers to unused fiber-optic cable, of which there is a glut thanks to a huge rush to install the cable in the early 1990s by telecommunications companies. Just as the cables were buried underground, the technology for transmitting data improved significantly so that fewer cables were needed. There are now dense corridors of dark fiber crisscrossing the entire country.

Distributed acoustic sensing (DAS) is a novel technology that measures seismic wavefields by shooting short laser pulses across the length of the fiber. “The basic idea is, the laser light gets scattered by tiny impurities in the fiber,” said Ajo-Franklin. “When fiber is deformed, we will see distortions in the backscattered light, and from these distortions, we can measure how the fiber itself is being squeezed or pulled.”

Using a test array they installed in Richmond, California – with fiber-optic cable placed in a shallow L-shaped trench, one leg of about 100 meters parallel to the road and another perpendicular – the researchers verified that they could use seismic waves generated by urban traffic, such as cars and trains, to image and monitor the mechanical properties of shallow soil layers.

The measurements give information on how “squishy” the soil is at any given point, making it possible to infer a great deal of information about the soil properties, such as its water content or texture. “Imagine a slinky – it can compress or wiggle,” Ajo-Franklin said. “Those correspond to different ways you can squeeze the soil, and how much energy it takes to reduce its volume or shear it.”

He added: “The neat thing about it is that you’re making measurements across each little unit of fiber. All the reflections come back to you. By knowing all of them and knowing how long it takes for a laser light to travel back and forth on the fiber you can back out what’s happening at each location. So it’s a truly distributed measurement.”

Having proven the concept under controlled conditions, the team said they expect the technique to work on a variety of existing telecommunications networks, and they are currently conducting follow-up experiments across California to demonstrate this. Ongoing research in Alaska is also exploring the same technique for monitoring the stability of Arctic permafrost.

Added Dou: “We can monitor the near surface really well by using nothing but traffic noise. It could be fluctuations in groundwater levels, or changes that could provide early warnings for a variety of geohazards such as permafrost thaw, sinkhole formation, and landslides.”

Using fiber for quake detection

Building on five years of Berkeley Lab-led research exploring the use of DAS for subsurface monitoring using non-earthquake seismic sources, Ajo-Franklin’s group has now pushed the envelope and has shown that DAS is a powerful tool for earthquake monitoring as well.

In the GRL study led by Lindsey in collaboration with Stanford graduate student Eileen Martin, the research team took measurements using the DAS technique on fiber-optic arrays in three locations – two in California and one in Alaska. In all cases, DAS proved to be comparably sensitive to earthquakes as conventional seismometers, despite its higher noise levels. Using the DAS arrays, they assembled a catalog of local, regional, and distant earthquakes and showed that processing techniques could take advantage of DAS’ many channels to help understand where earthquakes originate from.

Ajo-Franklin said that dark fiber has the advantage of being nearly ubiquitous, whereas traditional seismometers, because they are expensive, are sparsely installed, and subsea installations are particularly scarce. Additionally, fiber allows for dense spatial sampling, meaning data points are only meters apart, whereas seismometers typically are separated by many kilometers.

Lindsey added: “Fiber has a lot of implications for earthquake detection, location, and early warning. Fiber goes out in the ocean, and it’s all over the land, so this technology increases the likelihood that a sensor is near the rupture when an earthquake happens, which translates into finding small events, improved earthquake locations, and extra time for early warning.”

The research was funded by the Department of Defense through the Strategic Environmental Research and Development Program as well as by Laboratory Directed Research and Development funding.

Other co-authors on the GRL paper are Barry Freifeld of Berkeley Lab, Douglas Dreger of UC Berkeley, Martin and Biondo Biondi of Stanford University, Steve Cole of OptaSense Inc., and Stephanie James of Sandia National Laboratories. Lindsey is supported by a National Science Foundation Graduate Research Fellowship. Other co-authors of the Scientific Reports paper are Freifeld, Thomas Daley, Michelle Robertson, John Peterson, and Craig Ulrich of Berkeley Lab; Anna Wagner of the U.S. Army Cold Regions Research & Engineering Laboratory; and Martin.

# # #

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Filters

An international team of scientists --- including several researchers from the U.S. Department of Energy's (DOE) Argonne National Laboratory -- - has discovered an anode battery material with superfast charging and stable operation over many thousands of cycles.

Vector polarizers are a light filtering technology hidden behind the operation of many optical systems. They can be found, for instance, in sunglasses, LCD screens, microscopes, microprocessors, laser machining and more. Optical physicists published details of their new vector polarizer design this week in APL Photonics. The newly proposed design is a major advance in polarization technology because it enables flexible filtering of a wide range of light sources and generation of new light states.

Scientists have come up with a way to massively speed up the ordering process for self-assembling materials. The resulting ultra-small, well-ordered patterns could be used in the fabrication of microelectronics, antireflective surfaces, magnetic data storage systems, and fluid-flow devices.

Researchers from Stanford University, two Department of Energy national labs and the battery manufacturer Samsung created a comprehensive picture of how the same chemical processes that give cathodes their high capacity are also linked to changes in atomic structure that sap performance.

A new Petascale Data Transfer Node project aims to to achieve regular disk-to-disk, end-to-end transfer rates of one petabyte per week between major supercomputing facilities, which translates to achievable throughput rates of about 15 Gbps on real world science data sets.

Filters

NAU Regents' Professor Bruce Hungate, director of the Center for Ecosystem Science and Society (Ecoss), recently joined a new initiative lead by LLNL to study how the soil microbiome controls the mechanisms that regulate the stabilization of the organic matter in soil.

Scientists pause each afternoon at Kirtland Air Force Base in Sandia National Laboratories in Albuquerque, New Mexico, awaiting the daily lightning flash and unmistakable floor jolt that accompanies a Z shot

The University of Illinois at Chicago has received a five-year, $4.2 million grant from the U.S. Department of Energy to help industrial, commercial, institutional and utility entities evaluate and install highly efficient combined heat and power (CHP) technologies.CHP, also known as cogeneration, is a single system that produces both thermal energy and electricity.

ECS, in a continued partnership with the Toyota Research Institute of North America (TRINA), a division of Toyota Motor Engineering & Manufacturing North America, Inc. (TEMA), is requesting proposals from young professors and scholars pursuing innovative electrochemical research in green energy technology.

John Carlisle has been named the director of Chain Reaction Innovations (CRI), a program aimed at accelerating job creation through innovation, based at the U.S. Department of Energy's Argonne National Laboratory.

This fall, U.S. Department of Energy Secretary Rick Perry announced nearly $4.7 million in funding for the department's Argonne National Laboratory across 16 projects in three divisions. Four of those TCF awards, representing more than $1 million in funds, are slated for Argonne's Nuclear Engineering division.

Southern Research has been selected to receive nearly $1.7 million in U.S. Department of Energy funding to develop a new, cost-efficient gasifier capable of converting low-grade coal into synthesis gas (syngas) that can be used in a number of applications.

The world's most advanced particle accelerator for investigating the quark structure of matter is gearing up to begin its first experiments following official completion of an upgrade to triple its original design energy. The Continuous Electron Beam Accelerator Facility (CEBAF) at the Department of Energy's Thomas Jefferson National Accelerator Facility is now back online and ramping up for the start of experiments.